I'm not sure what you mean by that. The formula given in the link I posted, which I've tested by various ships (not all, admittedly) takes a ratio of the natural log of the total mass and the natural log of the thruster's optimal mass, so increasing the ship's total mass has a negative effect on speed.
Higher rated thrusters have a higher optimal mass value, thus are better.
Yes they require you to clamp the total mass yourself. One could rewrite the formula with a max line quite easily.
speed = base speed x (ln(thruster optimal mass) / ln(max(thruster optimal mass / 2, total mass)))
That's with four pips in ENG. Speed declines linearly with fewer pips, though at different rates. That's an area which needs more research. Boost is independent of pips; you either have enough capacitor energy to boost at full speed or you can't boost at all.
Thanks for your reply allow me to explain myself. (Sorry on phone so can't edit itby point easily)
Taking log(Optimum)base(current mass) scales significantly with mass (the value at 50% optimal mass decreases as optimal mass increases) this would imply smaller ships gain a greater benefit at 50% mass, my tests show no variation by ship mass however (tested sidey up to clipper).
On ratings, again my testing found that if you set up the same ship at 50% mass for each thruster ratings, A significantly out performs E rating at 50% mass. (~3% at E up to 16% at A) so it goes beyond just a higher optimum mass.
Thanks for clarifying the 50% self clamping didn't see it mentioned so thought i'd say.
Examples Vulture Class5A at 50% optimum =Log(840,420)~1.114 giving a speed of 234. My A rated vulture goes 244 (~1.16)
Clipper Class 6A at 50% gives log(1440,720) =1.105354 speed 332 (331.6 rounding). I clicked my A rated clipper at 348 (again~16%)
Hauler 2A log(36,72) = 1.19343 implies 239 max speed, actually only goes 232 (~16%)
