As I'm sure you know, the original SE5 had a fairly weak undercarriage, and at least one of the the prototypes (A4562, which later crashed when the wing failed in flight killing Major Frank Goodden, the accident eventually prompting the changes to the wing construction of SE5s) had to have its undercarriage replaced when being tested, so it was known that the undercarriage was a weak point, but what was also a problem was that the wheels were slightly too far rearward, so the load from the axles did not transmit directly up though the forward strut and thence up through the centre interplane struts, and it was more prone to nosing over on rough airfields.
It looks, on some photos, as though the undercarriage rake angle has changed as the SE5 has developed, but this is misleading, since at any sort of oblique angle, the outward splay of the undercarriage creates the impression of the strut having a forward rake, but it is always essentially straight up and down when viewed from the side. You can see that on these profiles:
What did change however, was the location of the axle in relation to that forward strut, which was indeed moved forward and can be seen sitting directly below the centreline of the later splayed out undercarriage strut type, which is where it would have sat on Ball's modified SE5. Albert Ball
had that done on his own SE5 whilst he was busy slagging the SE5 off in an attempt to promote his prototype which Austin were working on, but not all his bitching was selfishly motivated and that change to where the axle sat was one of several changes he made to the SE5 which were officially incorporated in the later production versions of the SE5, some were not, such as his relocation of the Vickers to sit on the cowling rather than in its more familiar enclosed location. You can see that undercarriage axle shift on the above profiles, where the centre of the wheel on the later versions is directly in line with the plumb line of the forward undercarriage strut.
Because of that, there are essentially three versions of the undercarriage on the SE5/SE5a, the early slim one, the later beefed up one, and the interim one where the struts are still the early type, but where the axle has been shifted forward. What adds to the confusion is the fact that quite a few SE5s were modified to incorporate changes (but not always all of them) to bring them up to SE5a standard. One such SE5 which is famous for having been through those changes is the early prototype, A4563. Cecil Lewis
ferried that aircraft out to France in June 1917, but, having been back at depots for repairs a few times during its operational service, it ended up with 84 Squadron in a much updated form. A4653 was actually successful in downing several aircraft, but it was written off in a take off accident in late February 1918, when being flown by Lt R E Duke. It apparently had just over 129 hours its the log when that crash occurred, which is quite a lot for a prototype and at the time it was struck off charge a couple of days later, alterations included the reduced wingspan of the SE5a, the addition of the Hispano Suiza 200hp engine, but still with the old style short exhausts and the earlier slim undercarriage type, making it a sort of SE5/SE5a hybrid, of which there were evidently quite a few.
For some decent pics on the late type SE5a undercarriage, you might want to take at look at this walkaround: