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

t=int(input())
for z in range(t):
    
    n=int(input())
    a = list(map(int,input().strip().split()))[:n]
    maxl=max(a)
    maxpos = a.index(max(a))
    flag=0
    for i in a:
        if i!=maxl:
            flag=1 
    if flag==0:
        print(-1)
        continue        

    if (a[maxpos-1]<maxl and maxpos>0) or (a[maxpos+1]<maxl and maxpos<n-1):
        print(maxpos+1)
        continue
    flag=0
    for i in range(n):
        if i>0:
            if a[i]>a[i-1] and a[i]+1>maxl:
                print(i+1)
                flag=1
                break
        if i<n-1:
            if a[i]>a[i+1] and a[i]+1>maxl:
                print(i+1)
                flag=1
                break
    if(flag==0):
        print(-1)
               
            





