Ah, the dreaded overlaps.
Non-megalithic culture/structures in prehistory(e.g. Iron Age forts, souterrains, brochs I guess). 'Romano-British' to 'Dark Age' (probably stopping at the time the English kingdoms became fully formed). Proto- to early Mediaeval (i.e. from coming out of the 'Dark Ages' until the Normans stopped being foreigners and started on England and Wales, which would cover perhaps barrows to mottes and stop short of castles proper). Neglected or obscure site-types generally.
Let's say two new camps basically. 1) That which TMA feels outside its remit and a time period to the withdrawl (sic) of the legions. 2) Early Christian to early Norman Conquest.
Just suggestions.