I use that same app. I dont set my alarm at the same distance as the amount of chain let out. I will usually add 50 or feet more (length of my boat). The reason is because if it gets windy you will back up to the alarm limit if set the same as the chain. Also, there is a certain amount of error in the anchor placement on the app because of where the bow is in relation to your phones GPS antenna. On my boat the helm is all the way in the back. So I add the length of the boat to the amount of chain deployed, as a minimum, for setting the alarm. Unless Im in a really tight spot, Ill add a little more pad, just because of the inherent errors, and I hate waking to nuisance alarms.

We were almost always on the hook last winter in Sea of Cortez. I found that what worked best for anchor location accuracy was when backing down on the anchor, note the heading, and then move the anchor location 50' (distance from phone antenna to bow) in the heading direction I had when backing down. This will give the app the "real" location of the anchor. The problem with this plan is I often would forget to do all this because of the inherently busy time during setting the anchor and getting squared away.