Dunno how it is now, but couple Patches ago when OBD increased the Twoseater/Scout ratio to a more realistic one, Bletchley's missions didn't seem to adapt the change, so possibly that when using those 3rd party missions, the ratio might be like it was before the fix. That means lot more scouts and lot less two seaters. But you may try of course.
The 3rd Party Mission Types don't specify aircraft ratios so they have the new Two Seater/Scout ratio also. The new ratios could be different based on mission type, and it is possible to change the ratio of mission types in the 3rd Party Missions, so that might be what you were seeing. For instance, you can set them up to produce more recon missions and less bombing missions (or vice versa) for two seaters. Or more or less balloon busting missions for scouts, etc. and if the two seater/scout ratios are different for different mission types that would be the only way the 3rd Party Missions could affect the ratio.
Two other "must have" mods would be Aris Clouds and Ankor Self Shadowing.
