OK, just back from happy hour (at 12:30am no less)... but I'll try to explain
the tips of the caps of 4's, 21's, 41's, etc are a bit further out than where the actual diaphrams of the 4V's are. The diaphrams aren't at the tip of the cap (on the V's), more towards the middle. That's where i got the 15cm estimate from. It's just an estimate though, could be closer to 17cm, or furthur away for that matter.
Now, the 70*... if you look at the 110* included angle, and put the caps backwards at 90* from that 110* you get 70* of included angle. It seems right on the bar, but actually look at the STC bar with caps on it, then put 2 straight edges at 90* (or side pickup, like the V's) and look at what you have. You can also do this on a peice of paper... just draw out a 110* angle (90* + a lil bit) and then draw 2 lines at 90* from each of them, your included angle will be less than 90* at 70*.
Either way, I like the tapes that are made this way, but I'm thinkin about trying the Vark bar out for some DIN and real ORTF with the 4V's in the near future.