Sion Ultimate Range Indicator

So I was watching S@20's Sion VO/SFX Preview when I couldn't help but notice that his ult range indicator follows him (as shown on the mini map). Wouldn't it make more sense for the indicator to be locked in place from the moment he starts charging until the end of the momentum? If this already isn't being working on, I'd like someone to take a look at it to see if something can be done. Currently I see no purpose of it following him as he has a maximum amount of time to charge.

However, I do not have access to the pbe so I'm unable to test a couple theories myself with it such as: Is it a set distance, or does the distance scale with movement speed?

If it were to be a set movement speed (such as his passive granting him a flat AS bonus which decreases if he has above 1.75 AS last time I checked) this would be practical for my idea of a locked indicator. Seeing as the max MS he gains is 950 in the video, I'm not sure if he can go beyond that with his ult or not. If he can go beyond the set distance, I suppose my idea is blown out of the water.

Anyone's thoughts on the idea of a locked indicator for the ultimate and can anyone test to see if the movement speed for me?