(Answered) Digging In/Hull Down & Trench/Fieldworks

[ShroudedSciuridae]

If a conventional infantry unit taking a turn for Digging In (add a +2 to-hit modifier, except for flamers and area-effect
weapons. No double damage in Clear hexes; TO:AR p. 106) does so in a prepared fortified hex (provides a +2 modifier to any attacks (except for flamers and area-effect weapons) made against any infantry unit that subsequently “digs into” the fortified hex; TO: AUE p. 153) are those modifiers cumulative to a +4 to-hit modifier?

The write up for fortified hexes says nothing about vehicles yet both Hull Down Vehicles (TO:AR p.19) and Turning Points: Tokasha track, Hitting the Wall (p. 14) say they can. So same essential question,  if a vehicle goes Hull Down in a fortified hex are those bonuses cumulative to a +4 to-hit modifier?

I would assume they are both cumulative, otherwise fortified hexes would provide no benefit at all.

[Xotl]

No.  Trenchworks provide a ready-made "dug in" position, but both trenchworks and digging in are the same modifier.  The only difference is that digging in requires the infantry to spend a full turn preparing its own position where it doesn't get the benefits until the next turn, and with trenchworks the infantry can move into the fortified position made by the engineers and immediately have the bonus.

But it's the same bonus, and not cumulative with itself.