Silverfish immediately begin suffocating when moving against a flowing water current

I was designing a silverfish grinder where they would spawn, then fall and land into a flowing water current that pushes them to a kill chamber. However, upon closer inspection I noticed that I was getting significantly less silverfish than I anticipated and realized it was due to the numerous amount of silverfish dying before reaching the drop off.

 

What I noticed was the following:

1. Silverfish spawn and drop into the flowing water current below
2. As soon as they land in the flowing water they begin taking suffocation damage

I could not determine whether or not the silverfish were pathing against the current but I get the impression that's likely the case given how there was still a fair amount that did make it to the drop off point without dying.

 

Additionally I tested this with other mobs such as zombies and skeletons however I could not replicate this issue with those, likely due to their height. So this issue likely has something to due with mob size as well.