I would opt unhesitatingly for the present perfect in nearly all sentences starting with since (when it is not used to mean for this reason).
Its usage nearly always covers a period from a point in the past up to the present, which is exactly what the present perfect signifies.
But your examples raise a question. If something has provoked questions since you started working there, the obvious constructions are either:
This has been the context of multiple questions I have asked since I started working here.
This is the context of multiple questions I have asked since I started working here.
If by was the context you mean that it is no longer the context, you might say:
This was the context of multiple questions I asked after I started working here.
This would indicate that it is no longer the context and the issue no longer bothers you.
I would add that the BBC appears to adopted a policy of using the past tense in its news bulletins in contexts where the present perfect is called for - and it never fails to jar on my ears.