Thanks for the prompt reply. Thats quite logical. Assassinating the early stacks before turn 10 resulted in extra stacks from HRE and France being sent.

I would have been better building forts and staging delaying tactics before sending my assassins in at turn 11 from crusade call.

I presume Jihad works the same way. (I jihaded against Marseille and fought some battles with sundry other lurking enemy stacks near Toulouse with the jihadis, whilst they were on their way to Marseille.)