The man implementation from mandoc does not adjust its output size to the terminal. As this is nice to have on smaller screens such as Termux we patch this in using the following patch adapted from

https://groups.google.com/forum/#!topic/fa.openbsd.tech/AEDMaZmzSU4

diff -u -r ../mdocml-1.13.4/term_ascii.c ./term_ascii.c
--- ../mdocml-1.13.4/term_ascii.c	2016-07-14 07:13:40.000000000 -0400
+++ ./term_ascii.c	2016-09-26 18:06:08.339737451 -0400
@@ -18,6 +18,7 @@
 #include "config.h"
 
 #include <sys/types.h>
+#include <sys/ioctl.h>
 
 #include <assert.h>
 #if HAVE_WCHAR
@@ -64,12 +65,22 @@
 	char		*v;
 #endif
 	struct termp	*p;
+	struct winsize	ws;
+	int		tfd;
 
 	p = mandoc_calloc(1, sizeof(struct termp));
 
 	p->line = 1;
 	p->tabwidth = 5;
 	p->defrmargin = p->lastrmargin = 78;
+	if ((tfd = open("/dev/tty", O_RDWR, 0)) != -1) {
+		if (ioctl(tfd, TIOCGWINSZ, &ws) != -1) {
+			if (ws.ws_col < 80)
+				p->defrmargin = p->lastrmargin = ws.ws_col - 2;
+		}
+		close(tfd);
+	}
+
 	p->fontq = mandoc_reallocarray(NULL,
 	     (p->fontsz = 8), sizeof(enum termfont));
 	p->fontq[0] = p->fontl = TERMFONT_NONE;