I go for the highest point (so the turbo coolant res). I also have the good old Lisley spill proof "funnel". That also works great. Put it on the turbo res, leave the rad cap off until you see the coolant getting close and cap it. Then add until it is full, but squeeze the hoses to bleed/siphon as plenty more will still go in. Heat it up until the fans come on. Let it cool. Check level and add as necessary. I should note that I perform this work with the car level and on the ground.
I have had my 02 Bugeye get air bound. It had only a rad cap on the turbo res (none on the radiator). Without the second cap, it can be a pain.
In your situation, I would just drain the radiator to "start over".