French language Q&A Forum

I am somewhat confused by one of your examples "Je suis assis entre Léa et Tim." The point of the exercise is not lost on me you are using the sentence to demonstrate the use of "entre". What puzzles me is the use of "je suis assis" which combines the present tense of etre "je suis" with the simple past of to sit "assoier". I'm obviously missing something obvious but it totally confuses me. I thought you had suggested that "I am sitting" and "I sit" can be  expressed by the same construction, the meaning altered by context; so why not "J'assieds entre Léa et Tim"?

the example here is 'De moins en moins de gens s'envoient des lettres' 

But in the A2 lesson on de moins en moins /de plus en plus with adverbes and adjectives it says that you can't start a sentence in French with 'De plus en plus'

Why is one sentence right in one context but not in the other? Is there a difference between using de plus en plus and de moins en moins at the beginning of the sentence? Or is it because the rule of not using de plus en plus at the beginning of a sentence is only when using an adjective or adverb? And if the later is the case does it apply to de moins en moins also? 

I used conte in my translation rather than the given "histoire," is there a difference between the two or are they completely interchangeable?