Distance to trader is calculated as a straight line. With clever (or infuriating design) you can make 70m seem like a hell of a long way.
My experience with KF-Farm was that distance didn't matter until wave 8 or so. Specimen spawn closer, more quickly, and in larger numbers. While on waves sub 8 you could sprint straight to the trader and defend, by the end there are so many crawlers that are literally on top of you within the first 15 seconds that not much sprinting happens. To counter act that you simply wait by the old trader spot, clear the wave, and run to the trader while the remnants of the wave chased behind you. Distance doesn't really matter there either.
But that's Farm. Farm is flat. When you make the space
between traders more complicated, all sorts of things happen. People get confused and turned around. Specimen get confused and turned around. The time to get from A to B increases, and distance in all three directions becomes really really important.
So it's really relative to your map design. What kind of map have you created? What's most 'fun' for your map and your personal style?
My biggest concern is how the distance impacts playability, should those who respawn be unable to beat the clock running to a far flung trader in time to re-arm.
Again, relative to map size and design. But I lean towards no. I like KF when it's more difficult, not easier. If you're doing the standard map design with one fixed respawn point, I would say at least 1 trader should be within "easy" distance. So getting to refill upon respawning would largely be luck.
KF-Prison to me a map that suffers from too much easy access. You can hit any of the traders, refill, and make it back to the camp spot with ease every time. BioticsLab is the same way. It gets repetitive. KF-Farm is good in that it forces you to move significant distances...but the open nature of the map either overwhelms players with attacks from every angle, or gives the sharp ones enough space to trivialize the horde through kiting and bunching.
Remember too, you reduce the need for traders by putting in more random spawns. If you do this don't make them too hard to find though. I think the mapping guide said most official KF maps have 15 spawns in them? That's the balance TWI decided to hit. There's no reason you can't put in a lot more spawns and make your traders more difficult to reach, and see how people like that balance. Personally, I like a little more 'horror' in my survival horror. My heart still misses a beat when I'm smacking my fire button and all I hear is "click click click". There needs to be more of that in KF maps IMO.