But there is in this game, fortifying over the cap.
The cap applies to the system upgrading to the next level of reinforcement (Exploited > Fortified > Stronghold); it can't upgrade more than one tier per cycle. But when it comes to the tug-o-war bar, additional reinforcement score beyond the weekly upgrade cap is still counted against any undermining score. So it is
not wasted merits as long as one values defending their systems.
Here's the proof through math:
Per
@Danieros'
screen shots of the Barnard's Star end-of-cycle scores, Aisling had amassed 1,523,747 reinforcement score while Archer had tallied 1,554,650 undermining score.
Based on the white marker, Aisling had started the cycle
at the point where the system had become Acquired and moved into the the Exploited category. So that's our starting point; our zero mark.
To move an Exploited system to Fortified requires 333,000 reinforcement control points.
A few hours prior to cycle end, Aisling had racked up 1,474,529 reinforcement control points while Archer had 1,059,806 undermining control points; a difference of +414,723 points in Aisling's favor.
On the tug-o-war graphic we see this accurately reflected: Aisling has filled the entire Exploited zone of the bar (333,000 controls points) and then pushed a little into the Fortified zone with the remaining surplus of 81,723. She can't leap frog two tiers in one cycle (Exploited + Fortified), but those extra points are still taken into account with regard to the fight playing out on the tug-o-war bar, as will be demonstrated.
We move to the end of the cycle where Archer beats Aisling's score 1,554,650 to 1,523,747, respectively; +30,903 in Archer's favor. This pushes the yellow tug-o-war tracking marker slightly to the left of the white starting marker, down into the Unoccupied portion of the bar. The amount of control score required to Acquire a system is 120,000 Merits. Make note of that as it's critical to an understanding of what is to follow.
Now, if what you and
@Danieros are claiming were true (fortifying over the cap is "wasted merits"), then Aisling's reinforcement control score would have capped out as soon as it reached the right-most end of the Exploited portion of the tug-o-war bar. In other words, no further Merits contributed to Aisling's reinforcement effort would have been counted against Archer's undermining; only the first 333,000 to go from zero Exploited to fully Exploited.
That means, with Archer's undermining score - which suffers from no cap - of 1,554,650 control points, not only would he have erased Aisling's gain of 333,000 reinforcement control score from the right-most, fully Exploited mark down to the left-most zero Exploited mark, he would have
ALSO completely annhilated the original Acquisition score of 120,000 Merits; with ample points to spare:
333,000 fully Exploited + 120,000 Acquired = 453,000 control points (Aisling's "cap" if what you are claiming were true)
1,554,650 (Archer's undermine score) - 453,000 (Aisling's "capped" reinforcement score) = 1,101,650 undermining control score in Archer's favor.
In this scenario Archer would have not only overcome Aisling's Exploited score, but would have blown her Acquisition score out of the water 9 times over! The yellow tracking triangle would have moved all the way to the left-most end of the tug-o-war bar's Unocuppied grey section.
BUT THAT'S NOT WHAT HAPPENED
Instead,THIS is how it was calculated:
Archer earned 1,554,650 undermining score, Aisling earned 1,523,747 reinforcement score:
1,554,650 - 1,523,747 = 30,903 points in Archer's favor.
This was enough to overcome Aisling's score, erasing her gains in the Exploited section of the bar (along with the spill over into the Fortified section), and push the yellow tracking triangle a bit into the grey Unoccupied section of the bar.
This is what we see reflected in the screen shots and that is how these scores are calculated.
The tug-o-war bar and the caps imposed on moving into the next tier of reinforcement (Exploited > Fortified > Stronghold) are DECOUPLED from one another. The weekly tier promotion cap does NOT impact the tug-o-war scores playing out between the two Galactic Powers. It is this fundamental misunderstanding of how these numbers are being calculated and the belief that one limits the other that is leading to the erroneous claim of "wasted merits" from "over reinforcing". They are two separate systems and calculations which - regrettably - are being represented through a single graphic, understandably leading to confusion.
Though the cap exists to prevent a Galactic Power from leap frogging ahead from zero to Stronghold status in one week, you better believe that if your opponent earns more undermining score than what your Galactic Power's current tier cap will allow only with respect to upgrading to the next tier, you better match or exceed it with your own reinforcing score if you want to hold onto the system.
The reinforcement control points which exceed the weekly tier cap won't allow you to prematurely advance to the next tier, but they WILL counter the undermining being applied to the system. Thus, there is no such thing as "wasted merits" or "over reinforcing" when it comes to defending your holdings against undermining (assuming you're invested in defending them in the first place).
EDIT: Added link to the Barnard's Star tug-o-war post for reference.