The upper limit is surface gravity, which is loosely connected to size. A procedurally-generated ELW cannot have more than 1.99 surface gravity. A low-density (rocky-ice) base planet can mean that a maximum-gravity ELW can be quite large. Hand-crafted ELWs in ED can get larger (with surface gravity much greater than 2.00), since the hard-cap restriction only applies to Stellar Forge generated planets.
Examples: the heaviest ELW in EDSM's database is the hand-crafted terraformed planet called "Tira Firble", in the Eurybia system: 7.1 Earth-masses, 10631 km radius and 2.56 G surface gravity. However, the largest ELW in the database is a proc-genned one, the fifth planet in the Boeph NN-J d9-131 system, a ringed world with only 4.97 Earth-masses, but at a much lower density giving it a 11914 km radius and 1.42 G surface gravity.
Again, don't forget the difference between an "Earth-like planet" in ED and an "Earth-like planet" in real-world scientific literature. ELWs in ED have a much narrower definition, where they have to have surface conditions that are survivable by a non-genetically-engineered human without a spacesuit. For real-world planetary scientists, all it needs to qualify as "Earth-like" is a solid surface.
ED certainly does reflect this theory, in that there can be very large life-bearing planets, for which the life is no doubt indeed protected by stronger magnetic fields, thicker atmosphere etc. However, in ED, such worlds are classified as "Water worlds". Or "Ammonia worlds", since those can get pretty big too. The EDSM records for heaviest WW and AW are 404 and 824 Earth-masses, respectively - both of which are more massive than Jupiter (only 318 Earth-masses).
We know that "atmospheric protection" does exist in ED as a factor for calculating the presence of life, from this one observation: every single ELW that is orbiting a neutron star has a very thick atmosphere. It presumably needs that thickness to shield it from the intense radiation coming from the neutron star. Or, to put it another way, the thick atmospheres existing in the face of extreme magnetic forces present around a neutron star indicate that those ELWs must likewise have extremely powerful magnetic fields, capable of shielding those planets.
