polymorphism - am I doing it right?

entity.clj

(defmulti tick (fn [e] (if (:tick e) :custom :default)))
(defmethod tick :custom [entity] ((:tick entity) entity))
(defmethod tick :default [entity]
  (-> entity
    (update-in [:x] #(+ %1 (:velx entity)))
    (update-in [:y] #(+ %1 (:vely entity)))))

(defmulti draw (fn [ctx e] (if (:draw e) :custom :default)))
(defmethod draw :custom [entity] ((:draw entity) ctx entity))
(defmethod draw :default [ctx {:keys [x y w h color]}]
  (set! (. ctx -fillStyle) color)
  (.fillRect ctx x y w h color))