Internal and external
Size vs mounting
In a perfect world for the wastegate, you should imitate a motorway exit. That is, exhaust gases coming from the engine towards the turbo must be smoothly directed towards the wastegate. Then you can have a small wastegate and do not have to compensate with the size of the wastegate due to a good flow.
But then it is not perfect for the turbo anymore as it is a large surface in the collector that creates turbulence and disrupts the flow. Here you have to compromise.
If you mount the pipe to the wg with a slightly sharper angle towards 90 degrees instead and compensate with a larger size of wastegate. Then you get a smaller connection area to the collector despite the larger wastegate. This setup does not interfere with the flow to the turbo as much when not in use and can still evacuate enough air.
However, the wastegate tube should never be angled in the opposite direction of the exhaust gases (above 90 degrees). Then you get both poor flow to the turbo and wastegate.