The ebps/impass_ext controls which entity type can pass through it. Set all values to True to block everything (in the gun). Don't set this in the pit, because it should let the gun 'pass' and that would cause other issues like what happend to the bofors.
The symbol height can be set in ebps/ui_ext/decorator_offset (in the pit). The value of 3.5 seems to put it in a normal height.
Big thanks! Your answers helped me much.
I also got issues in making pak 43 and lefh 18 emplacements using 25 pounder guide. Are there constructive differenses between actions with british and other factions' guns\howitzers?