IS-2 is facing Panther that have range 50.
Tiger starts with range 45 and face SU-85/M-36/FF with range 60.
You should be asking the same about the Tiger.
There is no reasoning behind tiger range buff in the patch notes and it got penetration buff in the same patch, I hardly doubt that both were needed since it was still a buff at a time when allied TDs did jack shit to heavy armor and Tiger already penetrated all of them 100% of the time.
Moreover, tanks should NOT be able to contest their own counters through range bonuses and that includes is-2 vs panther, however contrary to panther, allied TDs can't stand the pressure of Tiger dps against them, panther not only can take 2 more shots from IS-2, but can also deflect them.
Bonus range to help vs their own counter makes as much sense as giving brummbar 45-50 range, so it can stomp on ATGs easier.
Tiger more likely got bonus range to go up against Comets better, but since that time, comet was stomped into the ground and pounded some more through nerfs, so I'd argue 45 range for tiger at vet0 is no longer needed, vet2 bonus up to 50 is fine.