1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

for x in range(int(input())):
    n = int(input())
    m=list(map(int,input().split()))
    k=max(m)
    m.insert(0,k)
    m.append(k)
    #print(m)
    
    if len(set(m))==1:
        print(-1)
    else:
        r=0
        for i in range(1,n+1):
            if m[i]==k and (m[i-1]<k or m[i+1]<k):
                r=1
                print(i)
                break
        if r==0:
            print(-1)
    
    