A fine observation, Peter.  I'm prompted to explore Google and arrive at two significant links, one to a brief resume of Eliot's dramatic oeuvre, the other to a review of a study that makes a valuable addition to Eliot scholarship on this subject.

1. A Descriptive Chronology of Eliot's Plays, Theatrical Career, and Dramatic Theories 
    http://bingweb.binghamton.edu/~ccarpen/Eliot.htm 

2. "Where the Words Are Valid: T. S. Eliot’s Communities of Drama" 
    by Randy Malamud,  Westport, CT: Greenwood Press, 1994

http://www.jstor.org/discover/10.2307/3200884?uid=3739728&uid=2129&uid=2&uid=70&uid=4&uid=3739256&sid=47699118575027 

Regards,
  CR


From: P <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, July 5, 2012 5:51 PM
Subject: Re: Eliot on Marston

E. made a concerted study of Eliz. Drama early in his career in London which resulted in a whole series of such essays, all excellent, very readable and peppered with such important statements. All were preparation for his own poetic drama. The multileveled character of TWL suggested that was where he wanted to go. Sw. Ag. was the first result. MITC the next.

Collections of those essays are available as Elizabethan Essays.
P. M.

Chokh Raj <[log in to unmask]> wrote:

A genius that reflects in Eliot's works, both poetry and drama. 

CR


From: Chokh Raj <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, July 5, 2012 12:06 PM
Subject: Eliot on Marston

Contemplating John Marston

"It is possible that what distinguishes poetic drama from prosaic drama is a kind of doubleness in the action, as if it took place on two planes at once. . . .In poetic drama a certain apparent irrelevance may be the symptom of this doubleness; or the drama has an under-pattern, less manifest than the theatrical one. We sometimes feel, in following the words and behaviour of some of the characters of Dostoevsky, that they are living at once on the plane that we know and on some other plane of reality from which we are shut out: their behaviour does not seem crazy, but rather in conformity with the laws of some world that we cannot perceive. More fitfully, and with less power, this doubleness appears here and there in the work of Chapman, especially in the two Bussy D’Ambois plays. . . . //It is not by writing quotable "poetic" passages, but by giving us the sense of something behind, more real than any of his personages and their action, that Marston established himself among the writers of genius.//"  ('Selected Essays') 

CR