The reason it would make sense is because currently once you have upgrade, the more tommies you build the better, each extra squad decreases the shared cost of the upgrade = more for less.
But if you had to pey based on number of squads you have, it makes pure spamming more expensive, and a bit more combined arms rewarded.
If you felt the initial cost of the upgrade was to much you could just reduce the ammount of manpower you pay.
This would just be an indirect nerf to sappers
Bolster shouldn't have been touched until we get an entire UKF infantry rework similar to how OKW had Volks reworked. Otherwise it's just making UKF design even more sloppy and restrictive when the original design was one of choices and trade offs
Right now that choice is just being funneled into "upgrade bolster to survive", same with AEC and how Bofors tech doesn't really offer any AT. (Emplacement could have been moved and swapped with AT section package or something).
Brits needs some design overhauls not bandaids only to rip the bandaid half off next patch. This has been a cycle for a long time now thanks to relic not giving the balance team the greenlight to change emplacements and the mortar.