The Sefarim write that the Midah of Avraham was Chesed (kindness), the Midah of Yitzchak, Din (justice), and that of Ya'akov, Rachamim (mercy, synonymous with Tiferes) which is actually a blend between the two.

The Name Keil too, denotes Hash-m's Midas Rachamim (mercy), as Rashi explains in Shemos (34:6). True, Rashi also explains Hash-m as Midas ha'Rachamim, but I think that what he really means is Midas ha'Chesed (and this is borne out by R. Bachye, who also defines them both as Midas ha'Rachamim, only Hash-m is without Teshuvah, whereas Keil is only if one has asked for it (which seems to be the distinction between Chesed and Rachamim). To clinch this explanation, one has only to look at the wording of the prayer that we say for a deceased person 'Keil Malei Rachamim', which clearly indicates the connection between the Name Keil and the Midah of Rachamim.

I think that, having said that, the question is automatically answered.

Why, one may well ask, call Ya'akov by a Name of G-d at all?

I think that this is due to what I wrote above. Avraham and Yitzchak were also part of the Merkavah (the 'chariot of G-d'. In other words, they supported Hash-m's Throne). That is because they all but shed every vestige of earthliness, rising to a higher plane than the rest of mankind. However, in spite of the tremendous level that they reached, Avraham's Midas ha'Chesed was not tempered (which is why he had a son called Yishmael). And the same applies to Yitzchak, whose Midas ha'Din was extreme (which explains why he had a son called Eisav). Only Ya'akov, who inherited these Midos form his ancestors, molded them and perfected them, to reach a measure of perfection that his father and grandfather did not attain. That is why his children were all Tzadikim ('Mitaso Sheleimah').

Yes, Ya'akov reflected G-dliness to such a degree that Hash-m conferred upon him the Divine title, Keil (in a similar way that he would later refer to Moshe as 'Ish ha'Elokim'). And this also explains why it is the image of Ya'akov that did not only support Hash-m's Throne, but was also engraved underneath it. So much so that when the Angels heard that Ya'akov was asleep at the foot of the ladder, they came rushing down to take a look at the Tzadik with whose image they were familiar, but whom they now had the opportunity of seeing in the flesh.

Be'Virchas Kol Tuv

Eliezer Chrysler