Insight Maker doesn’t complain because its simulation engine is smart enough to convert the myriad of similar dimensions, e.g., miles, kilometers, feet, etc. However, it’s best to make conversions explicit, otherwise models become very difficult to understand.
One alternative would be to start with Distance to Grandmas House = 0 and add to the stock as Red walks toward it. This way the model is tracking the distance traveled rather than the distance remaining.
It takes time for a flow to change a stock and even longer for that flow to change a flow. It’s important to remember that reducing a flow still adds to the stock, just a bit slower.
There are actually two approaches: 1) Figure out how to shorten the delay; or 2) Slow down the action and wait for the feedback before further action. There are times when these approaches may be applied. Due to the nature of the situation there are other times when you simply need to act and then deal with the effects later.