One part of this problem is there since the balance patch last year, now an mech or HM can be very fast compared to an hauler.
But several other factors determine the speed a caravan closes up.
If you observe a caravan NPC group passing by, you could notice, that usually none of them moves straight line with full speed. The larger the group, the more obstacles on terrain the more they have a zigzag course. This zigzaging allows you to be faster on long term and only if they sprint towards you, you loose. This changed in my feeling since 3.7.1 patch on gamma to be less zigzag. I assume that your modification of terrain blocking has this side effect.
Before the 3.7. patch, the island layout on beta had several implications on the Obs way that lead to the fact that you could easier get out of their way.
All these points summed up lead to an overall increased problem where we had no problem one year before and now step by step unless it feels like a problem as the moment you see obs on your radar might be the moment you already lost your bot. If you move with half the speed of them you can only escape if you manage to move sideways out of their path for more then ~400m in the time they close in.