Technically the subtensions or stadia stay the same as an angular reading. But yeah, I get what you're saying.
However, this is only true for a certain magnification. Vortex has a ballistics calculator that allows you to name you reticle, load your muzzle velocity data, bullet data, etc. and see where the stadia read at different magnifications. I played around with it a quite a bit a year or two ago but now I hardly use the BDC stadia and just try to keep shots to MPBR. I do occasionally use it to guesstimate a little drop but if the shot is far enough that I have to go past the first stadia, I just leave it. I'm mainly shooting wallaby as pest control so I've figured out an average that kill them quick. Only go out to 70-80m with the 22 and maybe 180m with the 223 (full load) or 120m max if shooting with trail boss load.
My main point was that any BDC, being an angular reading, will only be correct at various ranges depending on the external ballistics of the round you are using.
It's all just a ball park guess once you factor in vagaries such as judging range, scope mag setting, muzzle velocity, bullet weight and BC. Know your kill zones and what range and conditions you are capable of hitting them.
That said, it is good to know your gear.