Sesame tries not to make decisions for you. If you put the cursor in the 5th position, Sesame believes that that is where you want it. If you move using "Enter", the cursor will go to the beginning. That way it is your choice.

Yes, Sesame supports overwrite by highlight - not mode. Insert/Overwrite by mode was (and is) more of a user interface problem than a solution, in that users must remember what mode they are in, what mode is default (very dangerous if overwrite is the default), and switch modes (without contributing to their data) to be effectively editing. This is not sound ergonomics or by any objective measure: "ease of use". The only way it succeeds in "ease of use" is mild familiarity. It fails in time taken, number of keys pressed, and number of mistakes made.

Overwrite by highlight, decreases time taken, decreases keystrokes, and greatly decreases mistakes made in that the only portion overwritten is that portion explicitly selected.