Reducing timescale and range is certainly useful, if for no other reason than to make the missiles a bit less ... handwavy. Some other things would need to change as well, though. Increasing the number of combat turns from planet to jump limit would alter the balance for some scenarios. Reducing time scale by 10 reduces the range units by 100 - which means we'd need to declare the 100 diameter limit to be the 1 diameter limit. The 420 minute 21 turn 1G flight to a size A world's jump limit 1,600,000 km distant becomes a 42 minute 21 turn flight to a jump limit 16,000 km distant - assuming HG's 1200 second turns.
However, with weapon ranges reduced by a factor of 100, a planet becomes a rather large obstacle on the playing field. Basically you're saying the planet surface is one end of the map. Less forgiving than having a little planet and being able to say you dodged it vertically, though that's not an issue in an abstract game. Planetary defenses become a bit problematic*. Meson weapons effective range of 50,000 km becomes 500 km, which means they're only protecting a portion of the planet. The canon 5g6 missile has a range of 13,000 km - well, 9000 km, given they were originally envisioned for a 1000 second turn (which I guess makes them 5G5's for the 1200 second turn version).
Reducing range by 10 requires reducing time scale by the square root of 10, which is OK except the time unit's 379.47 seconds. Reducing range by 4 halves the time scale, which at least gives round numbers - 600 (or 500) second turns - but laser range is still somewhat absurd, as are the missiles. Reducing it by 25 cuts the time scale to 1/5, but again the planet's a rather big part of the playing field, though I guess you could fudge things a bit on a band system, declare they were aiming high or low vertically on the approach to avoid a collision with the planet.
*That does resolve a problem I've been having with the amount of planetary defense installations a planet can afford, and it also allows a settlement to have missiles for their own defense while letting smugglers or pirates hide out on the other side of the planet.