I have a distance of 4'1" (1245mm) between the uprights on my trailer. This gives about a 1" clearance either side of the end of the cradle. I found when sliding the TI on, the nose of the ama splayed out a little, so I allowed a bit extra in the width for this. A bungee attached to the padeyes on the ama nose bring the ama together and make loading easier.
Adding a rear third cradle has improved loading/unloading as it lines everything up, making it easier to slide the TI between the uprights. It also makes it easy to fit a cart when removing the TI as it supports the cantilevered hull really well.