Hi all,
First, I want to thank for all the replies and responses I got for my previous questions.

I have arrows of 2 types: Type A has field point and straight 4" vanes. Type B is slightly lighter (by 20gr), has fixed broadhead and RH helical 3" vanes. Same shafts.

The problem: At 20 yards, type A hits 7" left and above type B.

Vertical variation I can understand, but why is the HORIZONAL variation?

which one have you sighted in CB with ? usually a fixed B'head will plane if its large &has big blades vented or not. best to sight in with same size arrow and weight of field tips/bullet pts the same weight. then you see where your B'eads hit, shoot more than one B'head make them 2 on 2 arrows. that will let you see how they compare to each other.

lt couldbe the fletching difference, the helical could be stabilizing the arrow alot more efficently than the straight fletch which is correcting any irratic arrow flight faster/better as it leaves the bow and there for changes the POI at the target, try swapping tips between the two sets of arrows and see what happens

Try a smaller, 4 bladed broadhead like Slick Tricks mags. They tend not to plane as much as larger heads.

I agree with Cossack, sounds like the broadhead is planing. I can be caused by miss-alignment, lack of off-set or helical, launch attitude, too fast of an arrow speed etc. Try what Cossack suggests. I've seen slight differences of an inch or two but you're is quite a lot of difference.

20" crossbow arrows are a lot less stable than 30" vertical bow arrows. Using large fixed blade broadheads on crossbow arrows can be tricky. If all you do is bowhunt with your crossbow, sight it in with the broadhead of your choice that will group well at your expected shot ranges. If you shoot a lot and want your field points and broadheads to not be an issue as to POI, one sure way of achieving that with no hassles is to use a premium expandable head like NAP's. Problem solved.

On vert bows as well as crossbows the faster you to the more important the broadhead is. What broadhead are you using and how fast is your bow spitting the arrow out?

My broadheads are 4 blade Muzzy 100. Vented and not very large, but I too suspect planing is the problem.

However, I expected planing to cause vertical change in POI. How can it deflect the arrows horizonaly? and by that much? (7" at 20 yards). Did anyone encounter such?

My main concerned is not sighting in, but that this behaviour indicates something is wrong with the CB.

are you cocking by hand or using rope cocker or mechainical. if by hand then your not cetering string the exact same each time its cocked.

I forgot that you have a homemade bow. Any idea how fast the arrow speeds are? I've had broadheads that impacted up and over but no where close. Try slowing it down if you are much over 300 ft/sec.