Namely, in a sense an object is the character of the event which is its situation, but it only influences the character of other events.

Accordingly the relations of situation and influencing are not generally the same sort of relation, and should not be subsumed under the same term 'ingression.' I believe that this notion is a mistake, and that it is impossible to draw a clear distinction between the two relations.
For example, Where was your toothache?
You went to a dentist and pointed out the tooth to him.

He pronounced it perfectly sound, and cured you by stopping another tooth.

Which tooth was the situation of the toothache?
Again, a man has an arm amputated, and experiences sensations in the hand which he has lost.

The situation of the imaginary hand is in fact merely thin air.