I don't see elements of the cavalry within the entrenchments as having had an intentional support role. Most of Wingfield's Battalion was inside and could have provided any cavalry support Gardner needed. My strong feeling is that the men simply were in the wrong place at the wrong time so ended up besieged with everyone else.
There is an element of "hmm?" in the lack of a regimental designation for that flag. Can't begin to figure it out, though.
Art