Fix gutter brackets before plastic eave support tray?

[epsilonGreedy]

Has anyone experienced a problem fitting gutter brackets to a fascia because of the drop of the eave support tray?

 

My fascia is only 120mm high and although the basic slate overhang and gutter fixing geometry should work in practice, the drop of the drip portion of the eave support tray is causing me problems.

 

I have only fixed 3m of eave support tray and so I am now considering fixing the gutter support brackets before fitting the eave support tray and slates. This would require some precise calculation to ensure the gutter and slate overhang will align nicely on completion.