Perspective from the air
The smallness of Shoreham airfield inevitably results in most of a fast-jet display being well outside the airfield boundaries, but there may be another problem from the pilot's viewpoint.
Without suggesting that it has any relevance to this particular accident, one of the significant features of Shoreham is the shortness of its only paved runway (about 3400 ft). Nothing unusual about that for the average GA pilot, but the resulting perspective from the air is very different from that at many airshow venues, not to mention the airfields where fast jets have to be based. If the runway is also narrower than the standard width at such airfields, as I think may be the case at Shoreham, a pilot could easily overestimate his/her height above the airfield when relying on visual cues. **
Some displays, of course, take place over grass airfields, farms, beaches, sea, etcetera (or even below cliffs). But in those cases the FJ pilot knows full-well that he is manoeuvring in a strange environment.
** I'm not suggesting that display pilots are not well aware of the above!